Image input apparatus and method

ABSTRACT

An image input apparatus. A detection section detects a change cycle of an intensity of an external light inputted to a camera. A timing control section synchronizes the change cycle of the intensity of the xternal light with a plurality of input timings of the camera by changing a phase difference in order. An evaluation section compares each storage quantity of the external light inputted to the camera at the plurality of input timings synchronized by the timing control section for each phase difference. A selection section selects the phase difference whose difference of the storage quantities of the external light is smallest from all phase difference changed by the timing control section.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an image input apparatus andmethod for correctly inputting a reflected light image of an objectwithout the influence of a change of external light such as afluorescent lamp.

[0003] 2. Description of the Related Art

[0004] In a computer system of the prior art, in order to virtuallygenerate a character model in three-dimensional space, a method forobtaining a distance image is well known, as shown in JapaneseApplication No. PH9-299648. In this method, first, a light is emitted toan actual object imitative of the character model. Second, lightreflected from the object is obtained and an image is generated by thereflected light. In this way, the reflected light image represents theshape of the object. In this case, the reflected light from a farbackground is very slight. Therefore, the shape of the object is easilyseparated from the background in the reflected light image. If theobject includes a reflected characteristic uniformly, this objectreflected light closely represents the three-dimensional shape.Therefore, the object-reflected light is transformed into athree-dimensional image. Furthermore, three-dimensional movement of theobject is easily extracted from a series of object-reflected lightimages. FIG. 1 shows, as one example, the reflected light image of ahuman's right hand.

[0005] In order to extract the reflected light image, the reflectedlight from the object is only detected without an external light such asan illumination light or sunlight. Therefore, image input operation isexecuted two times. At one time, a light is emitted to the object. Atthe other time, the light is not emitted to the object. The differencebetween the two images inputted at the two times is calculated as theobject-reflected light. These two input operations are executed at avery short interval, and the change of quantity of the external lightsbetween the two input operations is small. However, in an illuminationenvironment such as that created by a fluorescent lamp whose intensityis changing, the external light changes at very short intervals betweenthe two input operations. As a result, the quantity of the reflectedlight image falls because the shape of the object is not correctlyrepresented in the reflected light image.

[0006] Furthermore, in illumination such as that created by afluorescent lamp, the intensity basically changes in proportion to thecycle of the power supply. However, a waveform change is not clear as asine wave and partially includes an immediate change. In short, thewaveform change includes a harmonic. Therefore, in this case, thereflected light image includes the mixture of the shape of the objectand the change element of the external light.

[0007] Furthermore, if two input operations are simply executed at aninterval “10 ms” such as a flickerless operation of a CCD camera, thetime difference between the two input operations is long. In this case,if the object is moving quickly, the quality of the reflected lightimage falls. As for an LED used as an emission source, the shorter theemission time is, the brighter the LED momentarily emits by power.Therefore, if the stored time of the reflected light is long, the ratioof the external light to the reflected light is large and the dynamicrange to input the reflected light is narrow.

SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to provide an imageinput apparatus for correctly inputting the reflected light image of theobject without the influence of a change of the external light bydetecting the most suitable phase difference between the change cycle ofthe external light and the input timings of the reflected light image.

[0009] According to the present invention, there is provided an imageinput apparatus including a camera means for inputting an image of anobject, comprising: a detection means for detecting a change cycle ofthe intensity of an external light inputted to said camera means; atiming control means for synchronizing the change cycle of the intensityof the external light with a plurality of input timings of said camerameans by changing a phase difference in order; an evaluation means forcomparing each storage quantity of the external light inputted to saidcamera means at the plurality of input timings synchronized by saidtiming control means for each phase difference; and a selection meansfor selecting the phase difference whose difference of the storagequantities of the external light is smallest from all phase differenceschanged by said timing control means.

[0010] Further in accordance with the present invention there isprovided an image input method in a camera system for inputting an imageof an object, comprising the steps of: detecting a change cycle of theintensity of an external light inputted to said camera system;synchronizing the change cycle of the intensity of the external lightwith a plurality of input timings of said camera system by changing thephase difference in order; comparing each storage quantity of theexternal light inputted to said camera system at the plurality of inputtimings synchronized for each phase difference; and selecting the phasedifference whose difference of the storage quantity of external light issmallest from all phase differences changed.

[0011] Further, in accordance with the present invention, there isprovided a computer readable memory in a camera system for inputting animage of an object, comprising: an instruction means for causing acomputer to detect a change cycle of an intensity of an external lightinputted to said camera system; an instruction means for causing acomputer to synchronize the change cycle of the intensity of theexternal light with a plurality of input timings of said camera systemby changing a phase difference in order; an instruction means forcausing a computer to compare each storage quantity of the externallight inputted to said camera system at the plurality of input timingssynchronized for each phase difference; and an instruction means forcausing a computer to select the phase difference whose difference ofthe storage quantity of external light is smallest from all phasedifferences changed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic diagram of a three-dimensional reflectedlight image.

[0013]FIG. 2 is a block diagram of an image input apparatus according tothe present invention.

[0014]FIG. 3 is a schematic diagram of an image sensor in the imageinput apparatus of FIG. 2.

[0015]FIG. 4 is a flow chart of an image input method according to afirst embodiment of the present invention.

[0016] FIGS. 5A-5F are timing charts showing the relationship among achange of external light, a detected cycle signal and an operationphase.

[0017] FIGS. 6A-6G are time charts showing the storage operation of twotimes.

[0018] FIGS. 7A-7C are time charts showing the influence of change ofexternal light.

[0019] FIGS. 8A-8F are time charts showing an operation mode to evaluatean intensity of external light.

[0020] FIGS. 9A-9C are schematic diagrams showing a set of saturatedquantity in a stored section.

[0021]FIG. 10 is a flow chart of an image input method according to asecond embodiment of the present invention.

[0022] FIGS. 11A-11C are time charts showing an evaluation method forselecting the most suitable phase position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Embodiments of the present invention are described below withreference to the drawings. FIG. 2 is a block diagram of the image inputapparatus according to the present invention. An emission section 7emits light 16 at a predetermined timing supplied by a timing controlsection 4 through an emission control section 6. The emitted light 16reflects from an object 14 (a hand in FIG. 2). The reflected light 17 isreceived by an image sensor 12 through an imaging optical lens 13. Anoptical filter, not shown in FIG. 2, is located between the image sensor12 and the optical lens 13. Most of light wave length except for thelight from the emission section 7 are cut by the optical filter.

[0024] The image sensor 12 receives the light two times and outputs adifference between the two received light images in synchronization withemission. Therefore, the image sensor 12 outputs the object reflectedlight from the emission section 7 as the image.

[0025]FIG. 3 is a block diagram of the image sensor. In FIG. 3, eachlight-detecting cell 30 in the image sensor includes two capacitors 38and 40 that store electric charge. For example, one storage section 38stores the electric charge of light-detecting in case of emission, andthe other storage section 40 stores the electric charge oflight-intercepting in case of non-emission. A subtraction circuit 25outputs a difference between the electric changes stored in the twostorage sections 38 and 40.

[0026] In FIG. 2, the emission control section 6 and a control signalgenerator 8 generate signals for controlling the emission section 7 andthe image sensor 12. The timing control section 4 controls the emissioncontrol section 6 and the control signal generator 8. Output from theimage sensor 12 is converted to a digital image data by A/D converter 10through an analog signal processing section 11. The digital image datais used by a post-processing section not shown in FIG. 2 as thereflected light image from the emitted light.

[0027] In FIG. 3, each light-detecting cell includes two electric chargestorage sections as a customized image sensor. However, the image sensorof the present invention is not limited to the construction shown inFIG. 3. Actually, the same processing is executed by a CCD image sensormost frequently used, or by a CMOS image sensor loaded in a digitalstill camera recently. In short, the image sensor in FIG. 3 is regardedas a customized CMOS image sensor. A principle to obtain the reflectedlight is shown in Japanese Patent Applications No. PH9-299648 andPH10-31659.

[0028] In the present invention, two image input operations are executedat a predetermined interval. At one input timing of the two inputoperations, a light is emitted to the object. At the other input timingof the two input operations, the light is not emitted to the object. Thedifference between the two input images is output as the reflected lightimage of the object. In this case, if a change in the external lightbetween the two input timings affects the quality of the reflected lightimage, the technique of the present invention avoids this defect.

[0029] In the present invention, an external light detector 3, anexternal light cycle detector 1, a phase control section 2, and anexternal light influence evaluation section 9 are present as shown inFIG. 2. The external light detector 3 detects the quantity of externallight 19 such as the illumination light 15 or sunlight except for thelight from the emission section 7.

[0030] Furthermore, an optical filter to cut off the object reflectedlight 18 may be set in front of the external light detector 3. Theexternal light cycle detector 1 generates a change cycle signal of theintensity of the external light in response to the output from theexternal light detector 3. For example, in the eastern area from theKanto district of Japan, the intensity of the illumination light of thefluorescent lamp changes at cycle of “100 HZ”. Therefore, the changecycle signal of “100 HZ” is output. The phase control section 2 controlssynchronization between the emission section 7 and the image sensor 12in response to the change cycle of the external light. In this case, thephase control section 2 outputs a suitable trigger signal to the timingcontrol section 4 in order to synchronize the image input operation withthe cycle of the external light.

[0031] As mentioned-above, the reflected light image is obtained as thedifference between two images, one of which includes theobject-reflected light from the emission section 7. If the intensity ofthe external light does not change in the interval between the two inputoperations, the difference between the two images represents the correctquantity of the reflected light. However, in actuality, the intensity ofsome external light such as light from a fluorescent lamp often changes.In this case, the change in the external light in the interval isincluded in the reflected light image as noise. In order to avoid thisproblem, a cycle of the image input operation is made to be synchronizedwith the change cycle of the external light. Thus, at each timing of thetwo input operations, the intensities of the external light are alwaysequal.

[0032] For example, even if the intensity of the fluorescent lampchanges at the cycle of “100 HZ,” the intensity is not alwaysrepresented as a sine wave. Actually, in one cycle, the intensity byunit of time includes a large change part and a small change part.Therefore, in order to synchronize the cycle of the image inputoperation with the change cycle of the external light, thissynchronization is executed by a suitable phase difference. The phasecontrol section 2 changes the phase difference between the change cycleof the external light and the timing cycle of the image input operationsby a predetermined width. In order to achieve the most suitable phasedifference, the evaluation section 9 of influence of external light isused. The evaluation section 9 evaluates the change quantity of theexternal light between the two input timings for each phase difference.The most suitable phase difference is determined by using the evaluationresult. In general, the phase difference in which the external lightdoes not change at the two input timings is determined to be the mostsuitable.

[0033]FIG. 4 is a flow chart of the processing for determining the mostsuitable phase difference. First, a power supply is turned on as aninitialization process (S50). Then, a mode for measuring the influenceof the external light is set (S51). During the processing fordetermining the phase difference (S53˜S55), the emission section 7 doesnot emit light because only changes in the external light are evaluated.Next, in response to the cycle signal of the external light outputtedfrom the external light cycle detector 1, the cycle of the image inputtimings is gradually shifted in accordance with the cycle of theexternal light.

[0034] First, the phase difference between the change cycle of theexternal light and the cycle of two image input timings is set at aninitial position (S52). Concretely speaking, a first transition of aterm of the two input timings is made to coincide with a firsttransition of a pulse width of the change cycle of the external light.In this situation, the change quantity of the external light isevaluated and an evaluation result is stored (S53).

[0035] Next, the phase difference is shifted by a predetermined periodin order (S55) and the evaluation result of the change quantity of theexternal light is stored in the same way. This processing is repeateduntil the phase difference is shifted to an end position of the changecycle of the external light (S54). The most suitable phase difference isselected from all the phase differences by referring to each evaluationresult (S56). In this case, the phase difference in which the change ofthe external light between two input timings is smallest is selected.

[0036] However, as for the phase difference in which the change of theexternal light is smallest, if the change of the external light is largein a neighboring phase difference, this phase difference is not alwaysselected. If the change of the external light is small in apredetermined width of the phase, a phase difference at a centerposition of the predetermined width may be selected. After completion ofthese processings, a normal operation mode is set in order to obtain thereflected light image (S57).

[0037] In FIG. 4, the measurement mode of influence of the externallight is executed immediately after turning on the power supply.However, this measurement mode may be executed in response to a user'sindication. Furthermore, if this measurement mode is automaticallyexecuted at a predetermined interval, an accidental change of theexternal light is coped with. For example, some cases in which newillumination is supplied or a response characteristic of theillumination changes during time passing are coped with.

[0038] FIGS. 5A-5F are graphs showing the change of the external light,the change cycle signal and the cycle of the image input timings. FIG.5A shows one example of output from the external light detector 3. Theintensity of the fluorescent lamp basically changes in frequency twotimes in response to changes in the power supply frequency. However, thewaveform is not always a clear wave such as a sine wave. For example, apointed peak and a harmonic are included as shown in FIG. 5A. In casethe object-reflected light from the emission section is not attenuatedby an optical filter, the harmonic is generated in the waveform. Duringprocessing to determine the most suitable phase difference, the emissionsection 7 does not emit light and the reflected light is not incident tothe external light detector 3. However, after determining the mostsuitable phase difference, the emission section 7 starts emitting andsuch a pointed peak is generated. The external light cycle detector 1generates a cycle signal from the waveform. In this case, if thewaveform is converted to a pulse waveform by a predetermined threshold,the correct cycle is not obtained.

[0039] As shown in FIG. 5B, the harmonic is excluded from the waveform.The external light whose intensity changes is limited to the fluorescentlamp only and the signal of “100 HZ” or “120 HZ” is extracted as thecorrect waveform. Therefore, the waveform shown in FIG. 5A passesthrough a low-pass filter to cut off the higher frequency, and thewaveform shown in FIG. 5B is obtained. By converting the waveform inFIG. 5B to a pulse waveform, a cycle signal shown in FIG. 5C isobtained. In response to this cycle signal, timing of the image inputoperation is synchronized as shown in FIGS. 5D, 5E, and 5F. Two timingsof two input operations are included in each H level pulse. The phasedifference between the H level pulse of two timings and the change cycleof the external light is gradually shifted from FIG. 5D to FIG. 5F. Themost suitable phase difference is selected from all phase differencesaccording to each evaluation result.

[0040] FIGS. 6A-6G are detail time charts showing the input timings inFIGS. 5D-5F. As shown in FIG. 6A, assume that a first storage 73 and asecond storage 74 are executed in each H level pulse of FIGS. 5D-5F. InFIG. 6B and FIG. 2, a reset 75 of a photo diode 42, a reset 76 of thefirst storage section 38, a transfer 77 of electric charge to the firststorage section 38, a reset 78 of the second storage section 40, and atransfer 79 of electric charge to the second storage section 40 areexecuted in order. When the photo diode 42 is reset, the photo diode 42starts to store the electric charge photoelectrically converted, and thestored electric charge is transferred to the electric charge storagesection 38 (40) as a first image input operation. The electric chargestorage section 38 (40) is reset immediately before transfer of theelectric charge.

[0041] In order to reset the photo diode 42, a reset gate 35 is openedas H level by a timing shown in FIG. 6C and a transfer gate 41 is openedas H level by a timing shown in FIG. 6F. In order to reset the electriccharge storage section 38 (40), in addition to the reset gate 35, afirst sample gate 37 is opened by a timing shown in FIG. 6D, and asecond gate 39 is opened by a timing shown in FIG. 6E.

[0042] In order to transfer to the electric charge storage section 38(40), the transfer gate 41 and the first (second) sample gate 37 (39)are opened. The electric charge as a photoelectric conversion of theincident light is continuously stored in the electric charge storagesection from the reset of the photo diode to completion of the transfer.In the normal operation mode, when the emission section emits anemission control signal 80 shown in FIG. 6G, the first storage section80 stores the electric charge in case of no-emission and the secondstorage section 40 stores the electric charge in case of emission.

[0043] In the external light influence measurement mode, the emissionsection 7 does not emit light. As a result, the first storage section 38and the second storage section 40 respectively store the electric chargeof the external light only. In this case, ideally, the storage quantityof the two storage sections 38, 40 are equal. Therefore, in case ofemission, the reflected light of the object is correctly obtained as thedifference between the two storage quantities.

[0044] The relation between the two storage quantities and the change ofthe external light is explained by referring to FIGS. 7A-7C. In FIG. 7A,the change in the external light is represented as a curve 85, thestorage quantity in the first storage section 38 is represented as anarea 86, and the storage quantity in the second storage section 40 isrepresented as an area 87. If these two areas are equal, the phasedifference corresponding to the two areas is the most suitable. Thephase difference shown in FIG. 7B is the most suitable because thedifference between the two storage quantities is smallest. The phasedifference shown in FIG. 7A is not suitable because the difference istoo great.

[0045] As an output of the image sensor 12, the difference between thefirst storage quantity and the second storage quantity is output.Accordingly, if the second storage quantity is larger than the firststorage quantity, the difference represents the change of the externallight. However, if the first storage quantity is larger than the secondstorage quantity, the difference is output as a negative value. In caseof the negative value, the output of the A/D converter 10 is “0”. In anormal operation, a minus signal is not output and the negative signalis uniformly converted to “0”. Accordingly, for each phase difference, amode 1 by subtracting the first storage quantity from the second storagequantity and a mode 2 by subtracting the second storage quantity fromthe first storage quantity are prepared. The two differences for mode 1and mode 2 are evaluated. Alternatively, a negative-digital value isoutput for the negative signal, and an absolute value of thenegative-digital value may be evaluated.

[0046] In FIG. 7C, the first storage quantity 90 and the second storagequantity 91 are equal. However, the situation shown in FIG. 7B ispreferable to the situation shown in FIG. 7C. In case of directlydetecting the illumination light such as the fluorescent lamp, theelectric charge storage section 38 (40) is saturated by bright light. Ifboth the first storage section 38 and the second storage section 40 aresaturated, the difference is basically outputted as “0”. However, anirregular saturation in the storage section is actually output.Therefore, it is preferrable to execute the image input operation at thephase difference in which the intensity of the external light is small.In short, the most suitable phase difference is determined by not onlythe smallest difference between the two storage quantities, but also bythe low intensity of the external light.

[0047] In order to evaluate the intensity of the external light, anon-difference mode is set as shown in FIGS. 8A-8F. In FIG. 8A, thefirst storage section 38 does not store electric charge but is reset attime 100. The second storage section 40 only stores the electric chargeat time 99. This difference is output as the second storage quantity 99.In this case, the second storage period in FIG. 8A is half of the secondstorage period in FIG. 6A.

[0048] The reason for this is explained by referring to FIGS. 9A-9C. Innormal operation, the difference between the first storage quantity andthe second storage quantity is output and converted to digitalinformation by the A/D converter 10. In comparison with signal levelsaturated by the A/D converter, the saturated quantity in each storagesection 38 (40) is largely set because of the durability for theintensity of the external light. For example, as for maximum differencenot saturated by the A/D converter, a saturated quantity of four timesis previously set in each storage section 38 (40). In this case, even ifthe external light of three times the maximum reflected light, the imagesensor operates correctly.

[0049] In the normal operation mode, as shown in FIGS. 9A and 9B, thefirst storage section stores the external light 108, and the secondstorage section stores the external light 109 and the reflected light107. As shown in FIG. 9C, the difference 111 is output as a convertedvalue “0˜255” (8 bit in A/D). In this case, each saturated quantity 105,106 in each storage section is larger than the full quantity of A/Doutput. Accordingly, even if the external light 108, larger than thereflected light, is input, the reflected light is only extracted. Inother words, if the external light is stored during a period equal tonormal operation, the storage section is often saturated. In case thesaturated quantity of the storage section is set at four times normalquantity, the storage period is set at one fourth of the full storage ofthe saturated quantity. In this case, non-difference output is correctlymeasured. As a result, the intensity of the external light is evaluatedby the non-emission * non-difference mode shown in FIGS. 8A-8F.

[0050]FIG. 10 is a flow chart of the processing of a difference mode 1,a difference mode 2, and the non-emission•non-difference mode asmentioned-above. As for each phase difference, two images of theexternal light are inputted by unit of the difference mode 1, thedifference mode 2 and the non-emission•non-difference mode. The changeof the external light and the intensity of the external light for eachphase difference are evaluated.

[0051] In the flow chart shown in FIG. 10, a method to determine themost suitable phase difference is explained. As for the external lightshown in FIG. 11A, the larger output of difference mode 1 and differencemode 2 is shown in FIG. 11B and the output of thenon-emission•non-difference mode is shown in FIG. 11C. FIG. 11B shows agraph as an absolute value of differentiated output of a graph in FIG.11A. A graph in FIG. 11C is similar to the graph in FIG. 11A. First, inFIG. 11B, two phase positions 131 and 132 nearly equal to “0” areextracted as candidates of the most suitable phase difference. As for aphase position 132, the difference value becomes large if this phaseposition is slightly shifted. Therefore, in order to extract the mostsuitable phase difference, this phase position 132 is excluded. Next, inFIG. 11c, a phase part 133 in which the intensity of the external lightis small is selected. As a result, in FIGS. 11B and 11C, the phase part133 is determined as the most suitable phase difference.

[0052] In the above-mentioned embodiment, a normal fluorescent lamp ismainly assumed to be an external element. In case of an inverterfluorescent lamp in which the change period of the external light isshort, the present invention is applied. For example, as for theinverter fluorescent lamp, the intensity changes by a frequency of “40KHZ,” and one cycle of the change of the intensity is about 25 microseconds. In the image input apparatus of the present invention, atypical storage period per one time is about 2 milliseconds. In short,the storage period per one time includes eighty cycles of the change inintensity. In the case where an external light source is mainly theinverter fluorescent lamp, the influence of the change in the externallight is small. However, in an actual inverter fluorescent lamp, theintensity slowly changes by a power supply period during changing by “40KHZ” because the change of the power supply remains in the highfrequency signal generated by the inverter. If this slow change affectsthe external light, the image input apparatus of the present inventionis effective. In this case, the external light cycle detector 1 cuts offthe high frequency element by a low-pass filter, and only a cycle ofslow change remains. Therefore, this influence is excluded by theabove-mentioned processing based on the cycle of slow change.

[0053] Furthermore, if a phase difference for the change cycle of “40KHZ” appears to be an error, a cycle signal of the change cycle of “40KHZ” is detected at the same time, and a storage processing in thestorage section begins by a trigger such as a first transition of thecycle signal. By detecting both a cycle signal of “40 KHZ” and a cyclesignal of the slow change, a cycle of the image input operation issynchronized with the cycle signal of the slow change, and the timing ofthe first image input is executed by a trigger of a first transition ofthe cycle “40 KHZ.” In this case, the influence of the external lightfrom the inverter fluorescent lamp is greatly suppressed.

[0054] As mentioned-above, in the present invention, the change cycle ofthe external light is detected and the reflected light image is input insynchronization with the change cycle. In the measurement mode, wheneverthe phase difference between the change cycle of the external light andthe timings of the image input operation is changed by unit of apredetermined period, the change quantity of the external light isevaluated for each phase difference. Accordingly, the most suitablephase difference whose change quantity is smallest is selected from allphase differences, and the reflected light image is input insynchronization with the most suitable phase difference.

[0055] Furthermore, in the present invention, in order to determine themost suitable phase difference, the intensity of the external light isadditionally evaluated. As a result, the image input operation isexecuted during a period of relative dark external light. Therefore,even if the illumination light is directly input, the image is obtainedwithout saturation of the storage section. In the case of natural lightsuch as sunlight except for the fluorescent lamp, the durability of thestorage capacity is maximized.

[0056] In the above-mentioned embodiment, two images, one of whichincludes the object-reflected light, are input while the emissionsection emits light at the same time as the two input operations.However, the present invention is elective for all image inputapparatuses in which a difference between two images or two opticalquantities of an optical-detecting element are output. For example, amoving object and a stationary object are separated in the image bycalculating the difference between two images. In general, a part whosedifference is “0” represents the stationary object and a background, andthe part whose difference is a large value represents the moving object.In this case, if the change of the intensity of the illumination lightaffects the difference, the background is erroneously recognized as thmoving object. In order to avoid this probl m, the present invention isapplied.

[0057] Furthermore, the present invention is effective for an ordinarycamera apparatus. In case that a series of images such as a computervision is processed to extract some information, a change in theillumination light produces noise. In the present invention, the seriesof images without the noise of the change in the illumination light iseasily obtained in the same way as in the above-mentioned embodiment.

[0058] A memory device, including a CD-ROM, floppy disk, hard disk,magnetic tape, or semiconductor memory can be used to store instructionsfor causing a processor or computer to perform the process describedabove.

[0059] Other embodiments of the invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with the true scope andspirit of the invention being indicated by the following claims.

What is claimed is:
 1. An image input apparatus including a camera meansfor inputting an image of an object, comprising: detection means fordetecting a change cycle of an intensity of an external light inputtedto said camera means; timing control means for synchronizing the changecycle of the intensity of the external light with a plurality of inputtimings of said camera means; evaluation means for evaluating aninfluence of the external light inputted to said camera means at each ofthe plurality of input timings; and selection means for selecting one ofthe input timings whose influence of the external light is smallest fromall input timings.
 2. The image input apparatus according to claim 1,further comprising an emission means for emitting light to the object,and wherein said camera means inputs the image of the object at twotimes, and said emission means emits the light to the object insynchronization with one of the two times.
 3. The image input apparatusaccording to claim 2, wherein said camera means calculates a differencebetween two images inputted at the two times as a reflected light imageof the object by the light from said emission means.
 4. The image inputapparatus according to claim 2, wherein said emission means does notemit light during a measurement mode of the external light.
 5. The imageinput apparatus according to claim 1, wherein said evaluation meanscompares each storage quantity of the external light inputted to saidcamera means at each of the plurality of input timings, and wherein saidselection means selects one of the input timings whose difference of thestorage quantities of the external light is smallest from all inputtimings.
 6. The image input apparatus according to claim 2, wherein saidtiming control means repeatedly synchronizes the term of the two inputtimings with the change cycle of the external light by shifting the terminto the change cycle by a unit of predetermined phase difference. 7.The image input apparatus according to claim 6, wherein said evaluationmeans calculates a difference between two storage quantiti s of theexternal light inputted at the two input timings whenever the term ofthe two input timings is synchronized with the change cycle.
 8. Theimage input apparatus according to claim 7, wherein said evaluationmeans selects one difference which is smallest from all differences whencalculation of the difference is completed for all shifted terms.
 9. Theimage input apparatus according to claim 8, wherein said camera meansinputs two images at the two input timings of the term synchronized withthe change cycle as the phase difference selected by said selectionmeans in a normal operation mode.
 10. The image input apparatusaccording to claim 7, wherein said evaluation means evaluates onestorage quantity of the external light inputted at one of the two inputtimings whenever the term of the two input timings is synchronized withthe change cycle, and selects one difference if the one difference issmallest in all differences and the one storage quantity from which theone difference is calculated is below a threshold.
 11. An image inputmethod in a camera system for inputting an image of an object,comprising the steps of: detecting a change cycle of an intensity of anexternal light inputted to said camera system; synchronizing the changecycle of the intensity of the external light with a plurality of inputtimings of said camera system; evaluating an influence of the externallight inputted to said camera system at each of the plurality of inputtimings; and selecting one of the input timings whose influence of theexternal light is smallest from all input timings.
 12. The image inputmethod according to claim 11, further comprising the step of: emitting alight to the object in synchronization with one of two times when saidcamera system inputs the image of the object.
 13. The image input methodaccording to claim 12, wherein said camera system calculates adifference between two images inputted at the two times as a reflectedlight image of the object by the emitted light.
 14. The image inputmethod according to claim 12, further comprising the step of: stoppingthe emission of the light during a measurement mode of the externallight.
 15. The image input method according to claim 11, furthercomprising the steps of: comparing each storage quantity of the externallight inputted to said camera system at each of the plurality of inputtimings, and selecting one of the input timings whose difference of thestorage quantities of the external light is smallest from all inputtimings.
 16. The image input method according to claim 12, furthercomprising the step of: repeatedly synchronizing the term of the twoinput timings with the change cycle of the external light by shiftingthe term into the change cycle by a unit of predetermined pulsedifference.
 17. The image input method according to claim 16, furthercomprising the step of: calculating a difference between two storagequantities of the external light inputted at the two input timingswhenever the term of the two input timings is synchronized with thechange cycle.
 18. The image input method according to claim 17, furthercomprising the step of: selecting on difference which is small st fromall differences when calculation of the difference is completed for allshifted terms.
 19. The image input method according to claim 18, whereinsaid camera system inputs two images at the two input timings of theterm synchronized with the change cycle as the phase difference selectedin a normal operation mode.
 20. The image input method according toclaim 17, further comprising the steps of: evaluating. one storagequantity of the external light inputted at one of the two input timingswhenever the term of the two input timings is synchronized with thechange cycle; and selecting one difference if the one difference issmallest in all difference and the one storage quantity from which theone difference is calculated is below a threshold.
 21. A computerreadable memory in a camera system for inputting an image of an object,comprising: instruction means for causing a computer to detect a changecycle of an intensity of an external light inputted to said camerasystem; instruction means for causing a computer to synchronize thechange cycle of the intensity of the external light with a plurality ofinput timings of said camera system; instruction means for causing acomputer to evaluate an influence of the external light inputted to saidcamera system at each of the plurality of input timings; and instructionmeans for causing a computer to select one of the input timings whoseinfluence of the external light is smallest from all input timings.